Nitschke Hall

Research

Understanding and Predicting the Response of Cross-Laminated Timber subjected to a
TFE Event

Millions of Americans are daily exposed to the risk of a tsunami-following-an-earthquake
(TFE) event. Today, many US communities heavily rely on light-wood frame structures,
which are highly vulnerable to tsunami forces. There is an urgent need to rethink
the traditional civil infrastructure from a TFE perspective. The cross-laminated timber
(CLT) combines the advantages of wood with a high strength that is comparable to other
conventional alternatives such as reinforced concrete (RC).

This project will study the performance of cross-laminated timber (CLT) buildings
subjected to a tsunami following an earthquake (TFE) event (see the project framework
above). A novel holistic analytical model will be created from the experimentally
collected data. The created model will be used in a probabilistic study to create
fragility curves and evaluate the expected tsunami performance of CLT buildings (see
a sample fragility curve in the figure above). This study will contribute to the creation
of a tsunami-resilient design procedure for CLT buildings while helping our profession
and society progress towards designing tsunami-resilient communities. Project funding
is currently being raised to conduct this study. If you are interested in contributing
to this project, please contact Dr. Guner.

AN ANALYSIS METHODOLOGY FOR LESS-CONSERVATIVELY DETERMINING THE SHEAR CAPACITIES OF
OVERLOADED PIER CAPS

‘Pier caps’ or ‘bent caps’ transfer the load from the girders to the columns. In Ohio,
there are approx. 28,000 bridges with multiple pier caps for every bridge. When analyzed
using the slender beam theory, a considerable number of pier caps are found shear-overloaded
despite the fact that they don’t exhibit any noticeable cracking or signs of distress.
This casts some doubt on the currently used analysis methods for pier caps. Rehabilitating
all shear-overloaded pier caps will result in prohibitive costs. An accurate analysis
method is needed to obtain more realistic shear capacities to correctly identify the
overloaded pier caps.

The main objective of this study is to create a practical and accurate analysis method,
using the deep beam theory and the strut and tie method, for less-conservatively calculating
the shear capacities of pier caps. This method will be used to create a macro-based
analysis tool to generalize the findings and allow for applications in practice. The
outcome of this study will have a potential to result in: (1) significant cost savings
due to rehabilitating less number of bridges, (2) reduced construction work and associated
traffic congestion, and (3) reduced hazard to construction crews and traveling public.

A major challenge related to designing the next generation of civil infrastructure
is increasing their resiliency to natural hazards while ensuring a long-term and maintenance-free
service life. Helical piles are terminated with a cap plate, which is cast inside
concrete foundations. It is imperative that these connections perform well during
cyclic load reversals without resulting in any damage or cracking to the surrounding
concrete. The research objective is to advance the understanding of the effectiveness
of currently-used anchorage bracket types, quantify their load and deformation capacities,
discover any undesirable failure modes at ultimate load conditions, and propose readily-implementable
design details to improve their performance. The research findings will also be applicable
to micro piles and other steel piles with termination brackets.

Understanding and Predicting the Hurricane Response of Adhesive Anchors

Post-installed adhesive anchors are frequently used to attach non-structural components
(NSC), such as mechanical equipment, telecommunication antenna towers, balcony railings,
and solar panels, to concrete members. Damage reconnaissance studies demonstrate that
NSC damage accounts for a significant portion of the total hurricane repair costs
for buildings and that anchorage failures are the most prevalent failure mode for
NSCs. In addition to the financial losses, the failure of NSC anchors can potentially
result in: service interruptions, tearing of the roofing membrane and ensuing water
intrusion, high-speed wind-borne debris, delays in post-storm recovery, and, in some
cases, fatalities. Despite their frequent use, there is a critical gap in the current
knowledge for the dynamic wind load behavior of post-installed adhesive anchors.

This study aims to advance the current understanding of the dynamic wind-load behavior
of adhesive anchors, create and validate a high-fidelity computation simulation method,
and create a probabilistic analysis method to predict the risk of collapse. Project
funding is currently being raised to conduct this study. If you are interested in
contributing to this project, please contact Dr. Guner.

Every year, billions of dollars are spent in the US for repairing bridges; one of
the major causes of deterioration is the corrosion of traditional reinforcing steel
bars. As an alternative, FRP bars have excellent mechanical properties with a non-corrosive
material matrix. As such, they present a significant potential to extend the service
life and minimize the maintenance costs of concrete bridges. Despite the availability
of various types of FRP bars and design code provisions, there is a lack of numerical
modeling techniques to predict the load-deflection response and the failure mode of
concrete members containing FRP bars.

The objective of this study is to create a nonlinear finite element model to simulate
the response of concrete members containing FRP bars up to their failure. Numerical
modeling, reliability analyses, and experimental validation studies will be carried
out to advance the exiting knowledge and numerical modeling capabilities.

A New Modeling Methodology for Concrete Elements Retrofitted with Externally Bonded
FRP

Fiber reinforced polymers (FRP) are widely used in the retrofit of concrete elements
such as beams and columns. However, the system-level behavior of structures retrofitted
with FRP is currently not well understood, and there is a lack of numerical simulation
methods that can accurately account for the composite action and predict the structural
response. Thus, an efficient staged analysis approach with an accurate FRP modeling
methodology is required to provide a better understanding of the holistic structural
behavior.

In this study, a finite element-based staged analysis methodology is proposed for
deep beams retrofitted with externally bonded FRP fabrics (see the figure above).
A two-stage verification study was conducted, including: constitutive modeling of
critical material behaviors, and a full-scale structural modeling, both validated
with experimental results available in the literature. The proposed analysis methodology
was used to provide an effective retrofit solution for a real bridge bent and was
able to capture the improved beam response, as shown in the figures below.

Performance-based earthquake engineering (PBEE) requires a large number of nonlinear
dynamic analyses to statistically assess the performance of frame structures. The
complexity and high computational demand of such procedures has hindered its use in
practice. Simplified numerical modeling procedures can shorten the complexity and
computational demand. However, there is a lack of understanding on the accuracy and
reliability of the calculated responses from different numerical modeling techniques.
This research aims to fill this knowledge gap by using the experimental data to verify
the accuracy and computational demand characteristics of three different modeling
approaches (shown in the figure below).

Each created model has different levels of complexity and material behavior model
comprehensiveness. To evaluate their simulation accuracy and computational demand,
126 numerical simulations were performed for a previously-tested RC frame using a
PBEE framework. The accuracy of the calculated results was compared with the experimental
values in terms of the base shear and first-story drift (shear-drift figure above),
damage progression, and failure conditions. The computational demand of each model
was also evaluated in terms of required model development, analysis, and result acquisition
times. The influence of each modeling technique was compared using the calculated risk to
a set of performance limits evaluated by means of fragility curves. The nonlinear
models calculated significantly more accurate structural responses than the more-commonly
used plastic-hinge model. The model development and result acquisition times were
found to comprise a significant portion of the total computational demand of each
model (see the figure).

Creation of a Nonlinear Analysis Procedure for Frame Structures with Shear-Critical
Behavior

Although modern design codes require concrete buildings to be designed for ductile
and flexure-critical behavior, many older, shear-critical structures exist in practice.
Advanced nonlinear analysis methods with rigorous shear analysis capabilities are
required to identify and accurately determine the load-displacement capacities of
such frames. There is a critical gap in the knowledge for numerically simulating the
shear behavior of building frames.

In this study, an analytical procedure is formulated for the nonlinear analysis of
reinforced concrete structures consisting of beams, columns, and shear walls under
monotonic and pushover loads. The procedure is capable of accurately representing
shear-related mechanisms coupled with flexural and axial behaviors. The formulations
established include rigorous nonlinear sectional analyses of concrete member cross
sections, using a distributed-nonlinearity fiber model, based on the Disturbed Stress
Field Model (Vecchio, 2000). The proposed method is distinct from existing methods
in that it allows for the inherent and accurate consideration of shear effects and
significant second-order mechanisms within a simple modeling process suitable for
analyzing large buildings. Assumptions regarding the anticipated behavior and failure
mode of the system are not required.

Understanding and Modeling the Behavior of Beam-Column Connections

For Seismic Loading: Beam-column connections undergo significant shear deformations and greatly contribute
to story drifts during earthquake loading, yet their response is typically neglected
in traditional frame analyses through the use of rigid end offsets. Although local
joint models are available in the literature for the investigation of single, isolated
joints, there is a lack of holistic frame analysis procedures simulating the joint
behavior in addition to important global failure modes such as beam shear, column
shear, column compression, and soft story failures.

The objective of this study is to capture the impact of local joint deformations on
the global frame response in a holistic analysis by formulating a joint model into
an existing global frame analysis framework. The joint element can simulate the joint
shear deformations and bar-slip effects. Concrete confinement effects are also considered
so that both older and modern joints can be modeled.

For Progressive Collapse Loading: When a reinforced concrete frame is subjected to progressive collapse due to the
loss of a structural column, the surrounding elements typically experience a significant
overload that may lead to their collapse. The rotational capacity of beams and, consequently,
the beam-column connections is a critical factor determining the structural resiliency.
Numerical models developed to assess the structural response under a progressive collapse
situation must incorporate the beam-column joint response. In this study, a review
of the beam-column joint modeling approaches, constitutive models, and the ease of
their numerical implementation are presented. Some of these models are utilized to
simulate the response of a previously-tested reinforced concrete frame. The calculated
structural response parameters are compared to the experimental results, and the accuracy
of each constitutive model is evaluated.

Understanding and Modeling the Dynamic Behavior of Frame Elements

Subjected to Impact Loading: Heightened levels of terrorist threat have resulted in strategic structures, such
as government and commercial buildings, requiring design for blast and impact resilience.
Currently available methods employed in practice are typically based on overly simplistic
macro models, however, reducing each structural component to a single-degree-of-freedom
system. Moreover, the proper consideration of shear effects remains a major deficiency—
even in the micro-finite element methods—despite the fact that impact and blast loads
tend to result in significant shear damage. The objective of this study is to formulate
and verify a nonlinear frame analysis method capable of inherently and accurately
representing shear effects for elements subjected to impact loads. A second focus
is to account for the effects of the rate of loading within an explicit three-parameter
time-step integration method. Furthermore, verification studies were undertaken using
11 previously tested specimens.

Subjected to Earthquake Loading: Research studies conducted in the past number of decades have clearly demonstrated
the importance of ductility in the survival of frames under strong ground motions.
Modern seismic design codes, such as ACI 318, have thus incorporated stringent provisions
requiring structures to be ductile and flexure-critical in their behaviors; however,
many existing structures were constructed before the introduction of modern seismic
design guidelines with nonductile and shear-critical details. There is an urgent need
to perform safety assessments to identify and upgrade such structures. Currently available
dynamic analysis methods, however, typically neglect shear-related effects. This omission
may result in dangerously unconservative and unsafe response predictions. In this
study, dynamic analysis formulations are established and incorporated in an existing
global solution framework. The established method removes the current requirements
of the assumed failure mode and sectional response hysteresis model, and thus is suitable
for practical applications of seismic time-history analyses.

Subjected to Blast Loading: Recent bomb attacks on high-profile buildings have created an increased awareness
and demand for blast-resistant structures. The methods commonly employed for blast
load analysis are either based on overly-simplistic “single-degree-of-freedom” (SDOF)
approaches or overly-complex “finite element analysis” (FEA) software. SDOF approaches
have limited applicability and fail to accurately model the behavior of reinforced
concrete. FEA software is time-consuming, demands significant knowledge, and requires
a large number of customized input parameters for reliable results. This study examines
the accuracy, reliability, and practicality of a recently proposed analysis method
by modeling 18 previously tested specimens using only the default material models
and analysis options.

Creation of Computer Programs and Spreadsheet

To enable the research and engineering communities to use the established formulations,
a global simulation platform VecTor5 and a number of macro-enabled spreadsheets are
created. These tools enable the dissemination of research findings and permit understanding
the response of large, complete structures (as opposed the isolated structural components)
subjected to various loading conditions. Program VecTor5 incorporates more than 16,000
lines of numerical calculation algorithms, and are being updated as new material behavior
models and calculation methods are being created by the research team. Related Users’
Manuals and Bulletins are also composed by the research team to contribute to the
correct use of these numerical simulation methods.